Electron microscopy provides significant advantages over optical microscopy, such as higher resolution and greater depth of focus. In a scanning electron microscope (SEM) a primary electron beam is focused to a fine spot that scans the surface to be observed. Secondary electrons are emitted from the surface as it is impacted by the primary beam and some electrons from the primary beam are backscattered. The secondary or backscattered electrons are detected and an image is formed, with the brightness at each point of the image being determined by the number of electrons detected when the beam impacts a corresponding spot on the surface.
Electron microscopes are typically large, complex, and expensive instruments that require skilled technicians to operate them. SEM devices typically cost well over $100,000 and require special facilities, including dedicated electrical wiring and venting of the vacuum pump outside of the operator area. Further, it can be difficult in a high magnification image such as that of an SEM for a user to determine where on the sample an image is being obtained and to understand the relationship between that image and the rest of the sample. The cost of electron microscopes and the sophistication required to operate them have limited their use to research and industry that can afford the cost and provide the expertise to operate.
Because air molecules interfere with a beam of electrons, the sample in an electron microscope is maintained in a vacuum. After a sample is inserted, it typically takes a relatively long period of time for air in the chamber to be evacuated, so that a user must wait before an image is available. This delay makes use of an SEM impractical in many applications.
It would be desirable to provide a low cost electron microscope that can be operated by users that are not highly skilled and that could produce an image quickly after a sample is inserted.